Suppose a computer program needs to apply an affine transformation to a complex three-dimensional object made up of 7000 points. The transformation is composed of 7 matrices (call them through ), so for each point in the object, the following operation is performed.
Each multiplication of a matrix times a column vector involves 16 multiplications (of one number by another) and 12 additions, for a total of 28 arithmetic operations. Each multiplication of a matrix times another matrix involves 64 multiplications and 48 additions, for a total of 112 arithmetic operations. (These numbers are not made up or chosen randomly; they are facts about matrix multiplication.)

The most inefficient way of applying the transformation to the 7000 points would be to begin on the left, multiplying by , then that result by , and so on along the list from left to right, and doing the same 7 multiplications again for each of the 7000 points. How many arithmetic operations would this require for transforming one point?
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How many would it require in total for transforming all 7000 points?
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A more efficient method would be to start on the right, first multiplying by the column vector, then multiplying by that result, and so on, proceeding along the list from right to left.
How many arithmetic operations would this require for transforming one point?
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How many would it require in total for transforming all 7000 points?
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Using this method would therefore save what percentage of the time of the previous method?
Answer: %

The most efficient method would be to multiply the 7 matrices together and call that result (without yet multiplying by any column vector). After computing (just once of course), multiply by each of the 7000 points, each represented as a column vector.
How many arithmetic operations would it take to compute ?
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How many arithmetic operations would it require to multiply by one point?
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How many would this method require in total?
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Using this method would therefore save what percentage of the time of the previous method?
Answer: %

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